Re: [Qemu-devel] [PATCH RESEND 0/9] virtio: fix virtio child recount in transports

[Cornelia Huck]

On Fri, 26 Sep 2014 16:45:38 +0800
<address@hidden> wrote:

> From: Gonglei <address@hidden>
> 
> virtio-$device-{pci, s390, ccw} all duplicate the
> qdev properties of their virtio child. This approach does
> not work well with string or pointer properties since we
> must be careful about leaking or double-freeing them.
> 
> Use the QOM alias property to forward property accesses to the
> VirtIORNG child.  This way no duplication is necessary.
> 
> For their child, object_initialize() leaves the object with a refcount of 1.
> object_property_add_child() adds its own reference which is dropped
> again when the property is deleted.
> 
> The upshot of this is that we always have a refcount >= 1.  Upon hot
> unplug the virtio-$device child is not finalized!
> 
> Drop our reference after the child property has been added to the
> parent.
> 
> Attention please:
>  As Michael's comments, the patches will introduce regresion about
>  "-device FOO,help", which had been fixed by my other patch series:
>   [PATCH v2 0/7] add description field in ObjectProperty and PropertyInfo 
> struct
>  http://lists.nongnu.org/archive/html/qemu-devel/2014-09/msg04908.html
> 
> Acknowledgements:
>  I copied Stefan's commit c5d49db message about virtio-blk which
>  summarized reasons very well, I cannot agree more with him.
>  Holp Stefan do not mind, thanks!
> 
> Please review, Thanks a lot!

Do you have a git branch for quick testing?

> -Gonglei
> 
> Gonglei (9):
>   virtio-net: use aliases instead of duplicate qdev properties
>   virtio: fix virtio-net child refcount in transports
>   virtio/vhost scsi: use aliases instead of duplicate qdev properties
>   virtio/vhost-scsi: fix virtio-scsi/vhost-scsi child refcount in
>     transports
>   virtio-serial: use aliases instead of duplicate qdev properties
>   virtio-serial: fix virtio-serial child refcount in transports
>   virtio-rng: use aliases instead of duplicate qdev properties
>   virtio-rng: fix virtio-rng child refcount in transports
>   virtio-balloon: fix virtio-balloon child refcount in transports
> 
>  hw/s390x/s390-virtio-bus.c | 16 ++++++++++------
>  hw/s390x/virtio-ccw.c      | 18 +++++++++++-------
>  hw/virtio/virtio-pci.c     | 18 +++++++++++-------
>  3 files changed, 32 insertions(+), 20 deletions(-)

One thing I noticed is that the various devices end up with similar
code in the end:

     object_initialize(&dev->vdev, sizeof(dev->vdev), TYPE_WHATEVER);
     object_property_add_child(obj, "virtio-backend", OBJECT(&dev->vdev), NULL);
     object_unref(OBJECT(&dev->vdev));
     qdev_alias_all_properties(DEVICE(&dev->vdev), obj);

Would it make sense to add a helper function for that?